package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.text.Collator;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.util.StringHelper;

/**
 * Subclass of FilteredTermEnum for enumerating all terms that match the
 * specified range parameters.
 * <p>
 * Term enumerations are always ordered by Term.compareTo().  Each term in
 * the enumeration is greater than all that precede it.
 * @since 2.9
 */
public class TermRangeTermEnum extends FilteredTermEnum {

    private Collator collator = null;
    private boolean endEnum = false;
    private String field;
    private String upperTermText;
    private String lowerTermText;
    private boolean includeLower;
    private boolean includeUpper;

    /**
     * Enumerates all terms greater/equal than <code>lowerTerm</code>
     * but less/equal than <code>upperTerm</code>. 
     * 
     * If an endpoint is null, it is said to be "open". Either or both 
     * endpoints may be open.  Open endpoints may not be exclusive 
     * (you can't select all but the first or last term without 
     * explicitly specifying the term to exclude.)
     * 
     * @param reader
     * @param field
     *          An interned field that holds both lower and upper terms.
     * @param lowerTermText
     *          The term text at the lower end of the range
     * @param upperTermText
     *          The term text at the upper end of the range
     * @param includeLower
     *          If true, the <code>lowerTerm</code> is included in the range.
     * @param includeUpper
     *          If true, the <code>upperTerm</code> is included in the range.
     * @param collator
     *          The collator to use to collate index Terms, to determine their
     *          membership in the range bounded by <code>lowerTerm</code> and
     *          <code>upperTerm</code>.
     * 
     * @throws IOException
     */
    public TermRangeTermEnum(IndexReader reader, String field, String lowerTermText, String upperTermText, boolean includeLower, boolean includeUpper, Collator collator) throws IOException {
        this.collator = collator;
        this.upperTermText = upperTermText;
        this.lowerTermText = lowerTermText;
        this.includeLower = includeLower;
        this.includeUpper = includeUpper;
        this.field = StringHelper.intern(field);

        // do a little bit of normalization...
        // open ended range queries should always be inclusive.
        if (this.lowerTermText == null) {
            this.lowerTermText = "";
            this.includeLower = true;
        }

        if (this.upperTermText == null) {
            this.includeUpper = true;
        }

        String startTermText = collator == null ? this.lowerTermText : "";
        setEnum(reader.terms(new Term(this.field, startTermText)));
    }

    @Override
    public float difference() {
        return 1.0f;
    }

    @Override
    protected boolean endEnum() {
        return endEnum;
    }

    @Override
    protected boolean termCompare(Term term) {
        if (collator == null) {
            // Use Unicode code point ordering
            boolean checkLower = false;
            if (!includeLower) // make adjustments to set to exclusive
                checkLower = true;
            if (term != null && term.field() == field) { // interned comparison
                if (!checkLower || null == lowerTermText || term.text().compareTo(lowerTermText) > 0) {
                    checkLower = false;
                    if (upperTermText != null) {
                        int compare = upperTermText.compareTo(term.text());
                        /*
                         * if beyond the upper term, or is exclusive and this is equal to
                         * the upper term, break out
                         */
                        if ((compare < 0) || (!includeUpper && compare == 0)) {
                            endEnum = true;
                            return false;
                        }
                    }
                    return true;
                }
            } else {
                // break
                endEnum = true;
                return false;
            }
            return false;
        } else {
            if (term != null && term.field() == field) { // interned comparison
                if ((lowerTermText == null || (includeLower ? collator.compare(term.text(), lowerTermText) >= 0 : collator.compare(term.text(), lowerTermText) > 0)) && (upperTermText == null || (includeUpper ? collator.compare(term.text(), upperTermText) <= 0 : collator.compare(term.text(), upperTermText) < 0))) {
                    return true;
                }
                return false;
            }
            endEnum = true;
            return false;
        }
    }
}
